HERRIMAN, Utah — Authorities say a Utah wildfire ignited by Army National Guard members during weekend machine-gun training is 50 percent contained, and some evacuation orders have been lifted.

Fire officials said Tuesday evening that residents of about 200 homes in the Salt Lake City suburb of Herriman are being allowed to return. Evacuation orders remain in effect for another 250 homes near the fire's west flank — where officials say the 6-square-mile blaze was most active Tuesday.

Three houses were destroyed and a fourth was damaged after the fire started Sunday at Camp Williams. Authorities ordered the evacuation of more than 1,600 homes Sunday night.

Utah Army Guard Gen. Brian Tarbet has apologized for what he called a "systematic failure" that allowed guard members to conduct live-fire training exercises despite tinder-dry conditions and predictions of high winds at the base, about 30 miles south of Salt Lake City.

Police in Utah earlier told hundreds of families Tuesday they would be kept out of their homes for a third night. At that time the 6-square-mile fire was just 25 percent contained. Police Lt. Dwayne Anjewierden told reporters it was still too dangerous to let residents in the Salt Lake City suburb of Herriman return to about 450 homes closest to Camp Williams.

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Fire officials said the fire was burning scrub oak, sagebrush and cheatgrass, and said they feared winds could blow it north and east toward populated areas.

Tarbet said no one checked to see that the National Weather Service had posted a "red flag" fire warning before the machine gun exercise was permitted to continue in the foothills of the Oquirrh mountains. He also said guard commanders waited two hours to call outside fire agencies for help.

Administrators with the Unified Police Department, an agency overseeing Salt Lake County, said they recognized that the evacuation orders for parts of Herriman, a community of about 18,000, would cause hardships.

"We understand the frustration and how inconvenient it is to be forced from your home," police Lt. Don Hutson said.

The so-called Machine Gun fire was ignited at about 12:40 p.m. Sunday by practice rounds from a .50-caliber machine gun. Camp Williams, founded in 1926, covers 44 square miles — nearly twice the size of Manhattan.

Officials said a fire crew with a fire truck thought they contained the flames by about 1:30 p.m. Unified fire officials were called at 3:22 p.m., after flames began spreading fast.

"Our fire crews were on standby, responded and corralled the fire. They got it under control, but the winds came up, and the fire spread and got beyond what we could handle ourselves," McIntire said.

Overnight winds of more than 40 mph fanned the fire.

When the drill got under way, the National Guard said the fire hazard was moderate. There was little wind, temperatures were below 75 degrees, and humidity was 13 percent — typical for Utah's dry climate.

Fires caused by artillery shells or other weapons at military installations are not uncommon. In May 2007, a flare dropped from an F-16 on a training flight sparked a fire that burned 17,000 acres in New Jersey. Artillery practice sparked a huge wildfire in July 2009 outside Marseille, France.

At Camp Williams, a fire touched off by artillery burned 500 acres in September 2006 and forced the evacuation of about 50 homes. None were destroyed. A more recent fire burned 300 acres in July.

Utah National Guard officials said they can usually contain fires. But residents and Salt Lake County Mayor Peter Corroon questioned the National Guard's decision to hold live-fire exercises in dry conditions.

Hutson called the practice flare-up a "perfect storm" that kicked up violently with winds of 40 to 50 mph.

The fire has caused no major injuries, officials said, although two police officers were treated for smoke inhalation and a third for minor injuries after being hit by the vehicle of a driver trying to return home.

Video: Utah wildfire stemmed from spark at firing range

Transcript of: Utah wildfire stemmed from spark at firing range

BRIAN WILLIAMS, anchor:A wildfire sparked by
National Guard
troops training at a firing range has burned through 3500 acres in
Utah
. The fire started yesterday at
Camp Williams
, 30 miles south of
Salt Lake
.
Seventeen
hundred homes had to be evacuated. Forty to 50 mile an hour winds pushed this fire over a mountain ridge into a populated area.
National Guard
has suspended artillery practice at the base, and acknowledged tonight it was a mistake to train while red flag fire warnings were posted.